Academics have long thought that teams performed at about the average skill level of each of its members. So, at work, having a particularly skilled person on your team would help the performance a bit, and having a particularly unskilled or even lazy person would bring the performance down a bit.

That makes sense, but Walker's study suggests it's wrong. Walker first suspected this when he encountered a situation familiar to many of us. He and the other students were supposed to work in teams, and his team included, essentially, a freeloader: someone who did almost no work, but got the same grade as everyone else on the team. Then, when the team did relatively well, the freeloader did everything in his power to get assigned to the same team again.

So Walker designed a study. He gave 158 students a test designed to see how conscientious and motivated they were, and then sorted them into 33 teams. Each team was given a case study to work on, and was told that each team member would receive the same grade based on how well they did. He found that "the person who contributes the least has a huge impact. Even if the rest of the team is pulling their weight, they won't be able to compensate for that member." In the end, that single lazy person ended up with the most responsibility for team failure or success. Walker also ran tests to see if recklessness affected team performance, but found that the group mentality overrode the few impulsive people--in a way that it couldn't do with lazy folks.

What do you do when faced with someone who just won't pull their weight?

Kimberly Weisul is the co-founder of One Thing New, the free email newsletter for smart, busy women. She was previously Senior Editor at BusinessWeek, responsible for all coverage of entrepreneurship and for launching BusinessWeek SmallBiz, a bimonthly magazine. She is also a freelance writer, editor and editorial consultant.